Unable to group duplicated objects?
Add a Monkey (Shift+A)

Add a Circle (Shift+A) set the vertices say 10 or 12 (left hand panel or press f6)

Select the monkey and then the circle (order is important here)
Press ctrl+P -- object

Go to the object panel right hand in duplication section select verts

press ctrl+Shift+A then 

press ctrl+J